Apparatus for making solid carbon dioxide

ABSTRACT

Carbon dioxide snow from an overlying snow tower is intermittently fed into an extrusion chamber wherein a ram is reciprocated by a hydraulic drive. The snow is compressed at a pressure of at least 1 ton per square inch and extruded through a die having a plurality of apertures to make rods of dense supercooled CO2 that break into short nuggets. The size and number of the die apertures are controlled relative to the crosssectional area of the ram. A gas reservoir is provided in fluid communication with the rear end of the extrusion chamber which precludes the entry of humidity-bearing air into the cold extrusion chamber.

United States Patent [72] Inventor Lewis Tyree, Jr.

10401 S. Oakley Ave., Chicago, 111. 60643 [21] App1.No. 843,019 [22]Filed July 18, 1969 [45] Patented Jan. 4, 1972 [54] APPARATUS FOR MAKINGSOLID CARBON DIOXIDE 7 Claims, 2 Drawing Figs.

[52] US. Cl 425/378, 425/382, 425/405 [51] Int. Cl v. 1329f 3/00 [50]Field of Search 18/12 R, 12 P 56] References Cited UNITED STATES PATENTS1,919,698 7/1933 iis' i'i'igi.......III1IIIIIIIIIII 18/12 P 2,332,21110/1943 Field l8/12P Primary Examiner-Granville Y. Custer, Jr.Attorney-Fitch, Even, Tabin & Luedeka ABSTRACT: Carbon dioxide snow froman overlying snow tower is intermittently fed into an extrusion chamberwherein a ram is reciprocated by a hydraulic drive. The snow iscompressed at a pressure of at least 1 ton per square inch and extrudedthrough a die having a plurality of apertures to make rods of densesupercooled CO that break into short nuggets. The size and number of thedie apertures are controlled relative to the cross-sectional area of theram. A gas reservoir is provided in fluid communication with the rearend of the extrusion chamber which precludes the entry ofhumidity-bearing air into the cold extrusion chamber.

M MUJR ssmam APPARATUS FOR MAKING SOLID CARBON DIOXIDE This inventionrelates to the production of solid carbon dioxide and, moreparticularly, to a process for the production of solid carbon dioxidenuggets and to apparatus for performing such a process.

Solid carbon dioxide has the advantage of exceptionally good weightefficiency for a refrigeration media; however, the problems attendant toproviding usably shaped solid carbon dioxide at the point of end usehave thus far prevented solid carbon dioxide from attaining a very largeshare of the refrigeration market. Although solid carbon dioxide haslong been made available in the form of fairly large blocks, either asawing, pulverizing or a grinding operation has been generally requiredto reduce such blocks to a size suitable for the actual endrefrigeration use. Such operations both incur a labor cost for manpowerand give rise to a loss in the actual product due to increasedsublimation of the solid carbon dioxide during and after the operation.Although various attempts have been made to provide processes andapparatus for providing solid carbon dioxide in more usable form, nonehave achieved substantial commercial success.

It is the object of the present invention to provide an improved processfor providing solid carbon dioxide nuggets of a shape which facilitateseasy handling thereof and to provide apparatus for performing such aprocess. Another object of the invention is to provide a dependable,semicontinuous, automatic apparatus for the efficient production ofnuggets of solid carbon dioxide. These and other objects of theinvention should be apparent from a reading of the following detaileddescription of one illustrative apparatus embodying various features ofthe invention, in conjunction with the accompanying drawings wherein:

FIG. 1 is a vertical sectional view of apparatus for the production ofsolid carbon dioxide nuggets embodying various of the features of theinvention, which view is taken generally along section line 1-1 of FIG.2 and includes a diagrammatic representation of auxiliary equipment thatwould usually be included with such an operating apparatus; and

FIG. 2 is an enlarged front elevational view of the apparatus shown inFIG. 1.

An extrusion apparatus 11 is illustrated which is designed forautomatic, semicontinuous extrusion of a plurality of rods of densecarbon dioxide through apertures in an extrusion die 13. The apparatus11 includes a ram 15 which is driven in reciprocating movement by ahydraulic drive unit 17. In FIG. 1, the ram 15 is shown in its extendedposition in its location in an extrusion chamber 19 of the apparatus. Inthe extended position, the ram 15 blocks an entrance 21 to the extrusionchamber 19 from an upstanding snow tower section 23 wherein liquidcarbon dioxide is flashed to a mixture of carbon dioxide snow andgaseous carbon dioxide by expansion through a suitable nozzle 25. Thesnow falls to the bottom of the snow tower section 23 where itaccumulates until the ram 15 is retracted, at which time it falls intothe extrusion chamber 19 to be compressed by the ram on its next powerstroke. The downward flaring configuration of the inner wall of the snowtower section 23 helps assure the release of the snow, allowing it tofall by gravity into the extrusion chamber 19.

It has been found that by providing a hydraulic drive unit 17 which willapply sufficient force to said ram 15 so that the ram will exert apressure of at least about 1 ton per square inch upon the compactedsolid carbon dioxide at the end of the extrusion chamber 19, dense rodsof supercooled carbon dioxide are extruded. Moreover, it has been foundthat if a predetermined relative relationship is maintained between thecross-- sectional area of the ram 15 and the individual size and thetotal number of apertures in the extrusion die 13, efficient operationof the apparatus 11 in the extrusion of dense carbon dioxide rods isobtained. Inasmuch as the temperatures involved are well below thefreezing point of water, it has also been found important thathumidity-bearing air be excluded from the operational portions of theapparatus lest ice formation result which might well deter theperformance of the apparatus and/or require its shutdown. It has beenfound that, if the extrusion chamber 19 is closed to the atmosphere andif a separate auxiliary gas reservoir 27 of sufficient volume isprovided, entry of the atmospheric air into the extrusion chamber 19 iseffectively avoided.

Now referring more specifically to the details of the drawings, theillustrated apparatus 11 includes a base 29 upon which the extrusionchamber 19 is supported. The base 29 is hollow and also serves as thegas reservoir 27. The base 29 may be constructed in any suitable mannerto provide a gastight central chamber as by welding together two facingchannels and welding plates at the opposite ends thereof. A plurality offeet 31, suitably attached as with screw threads or by welding, supportthe base 29 above the level of the floor.

The extrusion chamber 19 is defined by an assembly comprising a mainhorizontal tubular body 33 containing the upper generally circularentrance 21 which is defined by an upstanding collar support section 35having a circular flange 37 at its upper end. The tubular body 33 ismounted on the base 29 by a rear mounting plate 39 and a front mountingplate 41.

The rear mounting plate 39 contains an annular cavity in the forwardsurface thereof which receives the rear end of the tubular body 33 and asuitable seal, such as an O-ring, may be disposed in the cavity to sealthe extrusion chamber l9 at this point from the outside atmosphere. Therear plate 39 is suitably secured to the base 29, as by a pair of boltsextending upward through the upper wall of the base into tapped holes inthe bottom of the plate. Two holes, which are drilled at right angles toeach other, provide a passageway 43 in the plate 39 extending from thefront surface of the plate downward to a tapped hole which receives thethreaded end of a pipe 43a that depends into the gas reservoir 27 in thebase. Thus the passageway 43 serves to place the reservoir 27 in fluidcommunication with the rearward portion of the extrusion chamber 19wherein the ram 15 reciprocates.

Coaxial with the ram 15 and extending from the left-hand side thereof(as viewed in FIG. 1) is a power transmission rod 45. Although the ram15 might be machined from a single piece of steel which would then besuitably attached to the power transmission rod 45, in the illustratedembodiment, the ram 15 is made, for manufacturing convenience, from aseries of separate rings 46 which are received on an end portion 47 ofreduced diameter of the power transmission rod. The individual rings 46are held in place by an endpiece 49 having a threaded central hole thatis screwed onto mating threads provided on the terminal portion of thereduced diameter section 47 of the power transmission rod. The threadedendpiece 49 is locked in place by a setscrew 51. A pair of front seals53 are received in a peripheral recess provided at the rear surface ofthe end piece 51 and in the region provided by making the forwardmostring 46 of a lesser diameter. A rider strip 55 is provided near the rearend of the ram 15, and no seal is provided at this location althoughthere is a fairly close sliding flt between the rear end of the ram andthe extrusion chamber wall.

The power transmission rod 45 extends through a central opening in therear mounting plate 39, and a seal and bushing assembly 57 is carried bythe rear mounting plate 39 to support, guide and seal the powertransmission rod at this location. The hydraulic drive unit 17 includesa double-acting hydraulic cylinder 59 which is connected by suitablevalving arrangement (not shown) to a source of hi gh-pressure hydraulicfluid, such as a motor-driven pump 61. The hydraulic cylinder 59includes a forwardly extending piston rod 63 which is coaxial with thepower transmission rod 45 and which is connected thereto via a suitableconnector assembly 65. The hydraulic cylinder 59 is also suitablysupported on the base 29 by mounting plates 67 and 69.

Disposed at the forward end of the extrusion chamber 19 is an expandingthroat member 71 which includes an upstanding circular flange of asuitable diameter to fit over the exterior surface of the circular frontend of the main tubular body 33. The inner surface of the throat member71 has the general configuration of a frustum of a cone, and it isemployed in order to provide a smooth transmission from the extrusionchamber 19 of a given diameter to the extrusion die 13 having anapertured region of a larger diameter. for reasons explainedhereinafter.

As best seen in FIG. 2, the extrusion die 13 comprises a generallyrectangular-shaped block of steel containing a plurality of apertures 73which are regularly spaced within a central circular region. Apertures73 of various shapes may be used; however, simple drilled holes areusually employed. The extrusion die 13 is machined to provide aprotruding short plug portion at the rear surface thereof which isreceived within the end of the throat member 71 as shown in FIG. 1. Theextrusion die 13 is supported by four threaded studs 75 extending fromthe front mounting plate using hexhead nuts 77 and suitable lockingwashers. The front mounting plate 41 is suitably attached to the base 29in the same manner as the rear mounting plate, as by upwardly extendingbolts. The front mounting plate 20 contains a central opening ofsuitable size to accommodate the front end of the main tubular body 33which passes therethrough. When the assembly of the structure iscomplete, four welded tie rods 79 are installed, using suitable nutswhich screw onto threaded portions thereof adjacent the front and rearmounting plates 39 and 41 and the hydraulic cylinder mounting plate 67,to add overall rigidity to the structure.

The snow tower section 23 comprises a generally tubular column 81 whichis designed to flt downward into the collar support section 35 andterminate a short distance above the upper surface of the ram at thelocation of the upper entrance 21 to the extrusion chamber 19. Aperipheral recess in the outer surface of the column accommodates asplit ring 83 which is seated in a suitable circular recess provided inthe upper surface of the upper flange portion 37 of the collar supportsection 35. The column 81 is clamped in this location by a holddown ring85 which contains a recess in its undersurface that receives the uppercircumferential edge of the split ring 83. Aligned holes in the holddownring 85 and the upper flange portion 37 of the collar support sectionfacilitate the attachment of the ring via nuts and bolts, and a suitableannular gasket is provided therebetween. The outer surface of the column81 is also provided with a pair of peripheral recesses which accommodateO-rings 87 that provide a seal between the outer surface of the columnand the inner surface of the collar support section 35.

The upper end of the column 81 is partially closed by a cap plate 89which carries a depending tube 91 leading upwardly to a central aperturein the cap plate 89. The cap plate is suitably attached by a pluralityof bolts which extend downward into the upper end of the column 81. Anupstanding internally threaded coupling 93, which is suitably attachedto the upper surface of the cap plate 89, provides a connection betweenthe top of the snow tower 23 and a gas return conduit 95. As best seenin FIG. 2, the nozzle 25 enters the column 81 in a nonradial directionso that the snow which is created is directed with a spiral motionagainst the inner wall of the column 81. This creates a centrifugalseparation effect with the solid snow tending to travel along the columnwall while the gaseous carbon dioxide remains primarily in the centralregion from which it exits by entering the bottom of the depending tube91, which leads upward and out of the top of the column 81 into thereturn gas conduit 95. Because spiral movement of the snow along thewall is created, an excellent separation of snow and gas is achieved asthe snow gravitates to the bottom of the column. As a result ofachieving such an effective separation, the nozzle can be operated at afairly high capacity.

In the overall operation of the extrusion apparatus 11, liquid carbondioxide from a storage vessel 101, whereat it is maintained at apressure between about 220 and 300 p.s.i.g., is fed to the nozzle 25through a feedline 103. If there is a considera ble distance between thestorage vessel 101 and the extrusion apparatus, a pump may be includedin the line 103. In order to subcool the incoming liquid, the feedline103 leads to a spiral coil of tubing 105 which is in heat exchangecontact with the outer surface of the column 81 which is made of amaterial, such as aluminum, that is a good conductor of heat. Thepassage of the relatively warm liquid through this spiral coil 105 hasthe dual effect of subcooling the liquid and warming the column 81,which further reduces any tendency the snow might have to adhere to theinner surface of the column and create a potential blockage. The liquidexiting from the coil 105 flows through a heat exchanger 107 where someof the cooling potential of the cold gas from the snow tower is utilizedto further subcool the liquid. From the heat exchanger 107 the liquidpasses through a valve 109 which leads to the nozzle 25. Properadjustment of the valve 109 provides the desired amount of flow ofliquid to the expansion nozzle 25 through which it is sprayed to createsnow and cold carbon dioxide gas at the rate desired.

The gas exiting from the upper end of the column 81 merges with gasflowing in a line 111 leading from the extrusion chamber 19 at a regionnear the right-hand end thereof where carbon dioxide gas is liberatedfrom the snow during the compressive action of the ram 15 on the snowcharge in the extru sion cylinder. Small holes in the wall of thetubular body 33 at this region lead to a circumferential cavity in thefront mounting plate 41 at the central opening therethrough. The cavityconnects via a drilled hole 113 with the line 111. The combined gasstreams pass through the heat exchanger 107 and pick up some heat fromthe liquid that is being subcooled. The cold gas from the heat exchanger107 flows through conduit 114 where it passes through a heat exchanger115 on its way to a compressor 117. The gas leaving the heat exchanger115 is at a pressure of about 30-40 p.s.i.g., and the compressor 117raises the pressure to slightly above 300 p.s.i.g.

The gas picks up a considerable amount of heat in the compressor 117,and it flows first through a water-cooled heat exchanger 119 on its wayback to the heat exchanger 115 wherein it loses more of its sensibleheat to the low-pressure cold gas stream flowing toward the compressor117. The highpressure gas exiting from the heat exchanger 115 flowsthrough a conduit 121 to a condenser 123 which is cooled by arefrigeration unit using a freon refrigerant. Freons are polyhalogenatedderivatives of methane and ethane containing fluorine and, in mostcases, chlorine or bromine. Monochlorodifluoromethane (Freon-22) is oneof the freons most commonly used. Refrigeration units of this type arecommercially available.

The condenser operation is controlled so that the gas is substantiallyentirely condensed to liquid before reaching a return line 127 leadingto the storage vessel 101. A pressure-regulating valve 129 in the returnline 127 maintains a pressure of at least about 300 p.s.i.g. in the line127. It has been found that the freon refrigeration unit functions farmore efficiently if the system is operated at a pressure of at leastabout 280 p.s.i.g. Most large CO storage vessel systems operate at apressure varying from about 240 to 280 p.s.i.g., depending upon supplyconditions and local climate; however, pressures are usually not usedabove about 300 p.s.i.g. Because the pressure within the usual storagevessel 101 does not normally exceed 280 p.s.i.g., it is not consideredeconomical to design the overall plant to function at much higherpressures. The pressure within the condenser 123 is preferablymaintained at a value of about 300 p.s.i.g. by the installation of thepre'ssureregulating valve 129 in the return line 127 that reads thepressure in the condenser via a pilot line (not shown). By operating thecondenser at such an elevated pressure, somewhat less heat need bewithdrawn from the compressed gas because the change to the liquid phasetakes place at a higher temperature. More importantly, this facilitatesthe higher temperature, more efficient operation of the refrigerationunit utilizing the joule-thomson expansion of freon refrigerant becausesuch units operate progressively less efficiently at progressively lowertemperatures where isenthalpic (joule-thomson) expansion departs moreand more from isentropic (perfect) expansion. The liquid passing throughthe valve 129 is delivered to the storage vessel 1111 at a locationabove the liquid level therein.

As previously indicated, the ram is driven in reciprocating movement bythe hydraulic drive unit 17 which includes the double-acting hydrauliccylinder 59. A suitable valving arrangement (not shown) is provided todrive the ram 15 forward on its power stroke until it reaches the pointof desired extension, which is shown in FIG. 1. At this point, thehydraulic fluid is shifted to the other end of the double-actingcylinder, and the ram 15 is retracted. As the front edge of the ram 15passes under the entrance 21 from the snow tower 23, the snow which hasaccumulated at the bottom thereof falls via gravity into the extrusionchamber 19 and continues to fall thereinto until the ram again closesthe entrance on its next power stroke. As the ram 15 moves forward, thesnow in the extrusion chamber 19 is carried along and compressed againstthe charge of solid carbon dioxide which fills the hollow re gion of thethroat member 71 adjacent the extrusion die 13. As compression of thesnow takes place, the gaseous carbon dioxide present escapes through theopenings in the extrusion chamber and exits through the hole 113 leadingto the line 1 11 which merges with the line carrying the gas leaving thetop of the snow tower.

As the ram 15 nears the end of the power stroke, the solid carbondioxide which has previously been built up in the throat member 71 isdisplaced by that being carried along by the ram and is thus forcedthrough the apertures 73 in the extrusion die 13 in the form of rods ofdense solid carbon dioxide. These rods are relatively fragile in tensilestrength and tend to break of their own weight to form short rodsections which are termed nuggets. If desired, a deflector (not shown)can be supported from the end of the extrusion die to assure thatbreaking of the rods occurs at about the desired length.

It has unexpectedly been found that the employment of the very highpressures which are available from the hydraulic drive system 17 notonly produces a dense product (which has good space efficiency, i.e.,B.t.u. per unit volume) but a supercooled product. It is found that asupercooling effect occurs when the ram 15 exerts a pressure of about 1ton or more per square inch against the built-up mass of solid carbondioxide in the throat member 71. The temperature depression of thenuggets results from the condition of very high compression which isestablished on the inlet side of the extrusion die while an essentiallyconstant temperature is maintained as a result of the presence of thefairly large mass of compressed solid carbon dioxide in the throatmember 71. When this high pressure is rapidly removed from the solidcarbon dioxide as the rods pass through the die apertures, supercoolingresults, The supercooling is quite advantageous because, as a result oftheir supercooled characteristics, the nuggets have and will retain goodstrength and handleability.

Generally, pressures of about 1.2 tons per square inch are employed. Inthe illustrated embodiment, the ram 15 has a diameter of about 6 incheswhich is equal to a cross-sectional area of about 28.3 square inches.The hydraulic drive unit 17 employed is sufficient to drive the ram 15with the force of about 70,000 pounds, or 35 tons, which is equal toabout 1.24 tons per square inch of ram surface area. Operation nearthese conditions has been found to produce nuggets from the extrusiondie which have a temperature as low as about 15 C. below the sublimationtemperature of solid carbon dioxide at atmospheric temperature, i.e.,75.5 C. (-1 10 F.

The number and the dimensions of the apertures 73 in the extrusion diecan be varied and have an effect upon the efficiency of the operation ofthe extrusion apparatus 11. For example, when x-inch diameter circularapertures 73 are employed, as was the case with the 6-inch diameter ramindicated above, the total cross-sectional area of the apertures shouldbe between about 70 percent and about 80 percent of the crosssectionalarea of the ram, and is preferably equal to about 75 percent of thecross-sectional area of the ram. For example, for a 6-inch diameter ram,this would be a cross-sectional area of about 25.5 square inches.One-half inch diameter apertures 73 individually have a cross-sectionalarea of about 0.196 square inch, so that 130 apertures are employed inthe extrusion die 13. in order to provide 130 56-inch diameter holes ina circular region and still retain sufficient strength in the steel dieto withstand the pressures which will be present in the ex trusionchamber 19, the outwardly tapering throat member 71 is employed whichflares outward to a circular opening having a diameter of about 8%inches. An extrusion apparatus 11 of approximately these dimensionsemploying a (3-inch diameter ram 15 having a stroke of about 12 inchescan be operated to reciprocate the ram through a complete cycle aboutevery 8 seconds, and under these conditions it will extrudeapproximately 700 pounds dense supercooled carbon dioxide nuggets perhour, which is considered to be very efficient performance.

As previously indicated, the relative relationship between the totalcross-sectional area of the apertures 73 to that of the ram 15 varieswith the diameter of the individual apertures. As set forth above, forapertures about one-half inch in diameter, it is considered that theapertures 73 should cover a total area equal to between about 70 percentand about percent of the cross-sectional area of the ram. Thisrelationship is inversely proportional. For slightly smaller apertures73, for example apertures about three-eighths inch in diameter, thetotal area occupied should be between about 80 percent and about 90percent of the cross-sectional area of the ram, and preferably equal toabout percent of the cross-sectional area of the ram for efficientperformance. For apertures slightly larger in diameter, for exampleabout five-eighths inch in diameter, it is considered that the totalarea occupied by the apertures should be between about 65 percent andabout 75 percent of the cross-sectional area of the ram, and preferablyequal to about 70 percent of the cross-sectional area of the ram 15 forefficient performance. it should be understood that the foregoingfigures are based upon simple drilled holes, and that if the dieapertures were formed to converge, i.e., have a decreasing diameter, alarger relative percentage of apertures would be used.

In summary, the illustrated extrusion apparatus 11 operates efficientlyin a semicontinuous, automatic fashion requiring little maintenancealthough temperatures in the neighborhood of 1 10 F. are experienced. Aswas previously pointed out, the extrusion chamber 19 is effectivelysealed from the humidity-bearing atmosphere. The charge of solid carbondiox ide which is built up in the region of the throat member 71provides a seal at the right-hand end of the extrusion chamber, asviewed in FIG. 1. The left-hand end of the extrusion chamber 19 issealed at the point of penetration of the power transmission rod 45 bythe bushing and seal assembly 57. The pair of O-rings provide a sealbetween the outer surface of the column 81 and the inner surface of theupstanding collar support section 35 at the point of junctiontherebetween. As previously indicated, the base 29 is made of acompletely welded construction so as to provide a gastight interiorchamber which serves as the gas reservoir 27.

As the ram 15 reciprocates within the extrusion chamber 19, it can beseen that the volume of the unoccupied region within the extrusionchamber varies from a maximum when the ram is in its extended position(as illustrated in FIG. 1) to a very small value when the ram is in itscompletely retracted position. The gas which fills this region betweenthe rear surface of the ram 15 and the forward surface of the rearmounting plate 39, unless accommodated during the retraction stroke ofthe ram, will be forced to bleed past the rear of the ram, which has afairly close sliding fit with the extrusion cylinder wall, and past thebushing seal assembly 57 in the rear mounting plate 39. Moreimportantly, when the ram moves forward on its next power stroke, avacuum would be created in this region that would result in gas bleedingback the opposite way. The gas which would bleed across the bushing andseal assembly 57 in the rear mounting plate 39 would be air from theatmosphere containing humidity. The water vapor in the air would turn toice when exposed to the very low temperatures within the extrusionchamber 19, resulting in lower efficiency of the apparatus operation andpotential maintenance and/or shutdown problems. These problems arealleviated in the illustrated extrusion apparatus 11 by providing thepassageway 43 which leads downward from the front face of the rearmounting plate into the reservoir 27 and provides for the simpleaccommodation of the dry gas which will occupy this changing volumeregion within the extrusion chamber 19.

By providing such a gas reservoir 27 of sizeable volume, the gas whichis forced from the left-hand end of the extrusion chamber 19 on theretraction stroke of the ram 15 is easily accommodated. The volume ofdisplaced gas which must be accommodated is equal to the differentialcross-sectional area between the ram 15 and the power transmission rod45 times the stroke of the ram, and the gas reservoir 27 should have avolume at least twice as large as this displaced gas volume. In theillustrated extrusion apparatus 11, the volume of the gas reservoir 27in the base 29 is about five times the displaced gas volume. Thus,assuming that the gas in the reservoir 27 and in the extrusion chamber19 is at some given pressure when the ram 15 is in its fully extendedposition, after the ram has moved to its fully retracted position, theincrease in pressure in the gas reservoir will be about 20 percent orless. This slight pressure increase does not result in any significantleakage past the bushing and seal assembly 57 during the short period inthe cycle when the ram 15 is near the end of its retraction stroke.

Thus, the invention provides a process for the semicontinuous productionof dense nuggets of supercooled carbon dioxide and apparatus forefficiently carrying out this process. One of the significant advantagesis that the production of such dense supercooled nuggets of solid carbondioxide produces an end product which is immediately ready for easystorage, distribution and handling at the use point for variousrefrigeration purposes. It is particularly advantageous that the nuggetsare flowable and thus are susceptible to handling in the same manner asother granular solids.

Various of the features of the invention are set forth in the followingclaims.

What is claimed is:

1. Apparatus for extruding nuggets of solid carbon dioxide, whichapparatus comprises means defining an extrusion chamber, a ram, ahydraulic drive unit connected to said ram for driving said ram inreciprocating movement within said extrusion chamber between an extendedposition and a retracted position, an extrusion die having a pluralityof apertures disposed at one end of said chamber, a snow tower disposedvertically above said chamber-defining means and opening downwardthereinto at a location between said die and said ram when said ram isin said retracted position, means as sociated with said snow tower forexpanding liquid carbon dioxide under superatmospheric pressure to formsnow into said extrusion chamber at a pressure of about 30-40 p.s.i.g.,the total cross-sectional area of said ram, being generally inverselyproportional to the size of the individual apertures, with circularapertures about five-eighths inch in diameter the total area of saidapertures being between about 65 percent and 75 percent of thecross-sectional area of said ram, and with circular apertures aboutthree-eighths inch in diameter the total area of said apertures beingbetween about percent and percent of the cross-sectional area of saidram, said hydraulic drive unit being designed to supply sufficient forceto said ram to compress said snow and extrude dense rods of supercooledcarbon dioxide through said apertures in said die.

2. Apparatus in accordance with claim 1 wherein the ratio of the totalcross-sectional area of said die to said cross-sectional area of saidram is about l. 9.

3. Apparatus In accordance with claim 1 wherein a rod for reciprocatingsaid ram extends exterior of said chamber-defining means at the rear endthereof opposite from that at which said extrusion die is disposed,wherein seal means is provided between said rod and saidchamber-defining means, and wherein gas reservoir means is providedwhich is in fluid communication with said extrusion chamber at alocation near said rear end thereof.

4. Apparatus for extruding nuggets of solid carbon dioxide, whichapparatus comprises means defining an extrusion chamber, a ram, ahydraulic drive unit connected to said ram for driving said rarn inreciprocating movement within said extrusion chamber between an extendedposition and a retracted position, an extrusion die having a pluralityof apertures disposed at one end of said chamber, a rod forreciprocating said ram extending exterior of said chamber-defining meansat the rear end thereof opposite from that at which said extrusion dieis disposed, seal means between said rod and said chamber-definingmeans, gas reservoir means which is in fluid communication with saidextrusion chamber at a location near said rear end thereof, a snow towerdisposed vertically above said chamber-defining means and openingdownward thereinto at a location between said die and said ram when saidram is in said retracted position, and means associated with said snowtower for expanding liquid carbon dioxide under superatmosphericpressure to form snow, said hydraulic drive unit being designed tosupply sufficient force to said ram to compress said snow and extrudedense rods of supercooled carbon dioxide through said apertures in saiddie.

5. Apparatus in accordance with claim 4 wherein said reservoir meanscomprises a hollow chamber sealed from the atmosphere having a volume atleast about twice as great as the differential cross-sectional areabetween said ram and said rod times the length of stroke of said ram.

6. Apparatus in accordance with claim 5 wherein said hollow chamber isformed by an elongated base whereupon said extrusion chamber-definingmeans and said hydraulic drive unit are physically supported.

7. Apparatus in accordance with claim 6 wherein said chamber-definingmeans includes a horizontal generally tubular member supported betweenfront and rear plates, wherein said seal means is carried by said rearplate and wherein said rear plate contains passageway means leadingdownward to said gas reservoir means in said supporting base.

2. Apparatus in accordance with claim 1 wherein the ratio of the totalcross-sectional area of said die to said cross-sectional area of saidram is about 1.9.
 3. Apparatus in accordance with claim 1 wherein a rodfor reciprocating said ram extends exterior of said chamber-definingmeans at the rear end thereof opposite from that at which said extrusiondie is disposed, wherein seal means is provided between said rod andsaid chamber-defining means, and wherein gas reservoir means is providedwhich is in fluid communication with said extrusion chamber at alocation near said rear end thereof.
 4. Apparatus for extruding nuggetsof solid carbon dioxide, which apparatus comprises means defining anextrusion chamber, a ram, a hydraulic drive unit connected to said ramfor driving said ram in reciprocating movement within said extrusionchamber between an extended position and a retracted position, anextrusion die having a plurality of apertures disposed at one end ofsaid chamber, a rod for reciprocating said ram extending exterior ofsaid chamber-defining means at the rear end thereof opposite from thatat which said extrusion die is disposed, seal means between said rod andsaid chamber-defining means, gas reservoir means which is in fluidcommunication with said extrusion chamber at a location near said rearend thereof, a snow tower disposed vertically above saidchamber-defining means and opening downward thereinto at a locationbetween said die and said ram when said ram is in said retractedposition, and means associated with said snow tower for expanding liquidcarbon dioxide under superatmospheric pressure to form snow, saidhydraulic drive unit being designed to supply sufficient force to saidram to compress said snow and extrude dense rods of supercooled carbondioxide through said apertures in said die.
 5. Apparatus in accordancewith claim 4 wherein said reservoir means comprises a hollow chambersealed from the atmosphere having a volume at least about twice as greatas the differential cross-sectional area between said ram and said rodtimes the length of stroke of said ram.
 6. Apparatus in accordance withclaim 5 wherein said hollow chamber is formed by an elongated basewhereupon said extrusion chamber-defining means and said hydraulic driveunit are physically supported.
 7. Apparatus in accordance with claim 6wherein said chamber-defining means includes a horizontal generallytubular member supported between front and rear plates, wherein saidseal means is carried by said rear plate and wherein said rear platecontains passageway means leading downward to said gas reservoir meansin said supporting base.